Currently displays that use organic light emitting diodes (OLED) are commercially available. For example, some Motorola phones and Norelco shavers have such displays.
Advantages of OLED displays over liquid crystal displays (LCD) are that there are no viewing angle limitations because each of the OLED pixels is self-emissive and so there is no need of backlighting as in an LCD.
Furthermore, researchers are experimenting with conductive polymers to form transistors, diodes, other circuit components, and circuits from these components.
Referring to FIG. 1, OLED modules are built using polymer technology. A module includes several deposited layers of different materials. Specifically, a transparent base material 1 is generally glass or Mylar or another transparent material. On this layer is deposited a transparent electrode 2, an emitting polymer layer 3, and an electrode 4. Light 5 is generated by the polymer layer 3 and is emitted through the transparent electrode 2 and the glass 1.
There are a number of existing manufacturing techniques for making both OLED displays and conductive polymer circuits. For example, polymers can be deposited in layers using chemical vapor depositions much like with semi conductor processing. However, this technique, although it has a high yield, is relatively expensive.
Also, ink-jet printer type deposition has been suggested as a manufacturing technique where different polymers are sprayed on in desired patterns. The polymers are sprayed onto a flexible substrate such as a paper or Mylar, which allows these circuits to flex and to be rolled up. The circuits can be “printed” on large rolls of paper that are then cut up to form individual circuits.
A problem with conductive polymer circuits printed onto a substrate is that the process, and thus the spacing of the polymer components, is dependent on the limitations of the printer. For example, it is known that ink-jet printers cause splatter and bleeding, which increase the size of a printed “dot”. This has not been a big problem with OLED displays, because the pixels are relatively large. But, when forming conductive polymer transistors, the relatively low resolution of ink-jet printers may limit the density of the resulting conductive polymer circuitry.
To put this potential density limitation in perspective, silicon transistors are now in the range of approximately one one-millionth the width of a human hair. But printer technology is merely in the 600 to 1200 dots-per-inch (DPI) range. Furthermore, because of splatter and the fact that devices such as transistors have different regions, e.g., source, gate, and drain, the actual number of transistors per inch may be significantly less than this, perhaps in the 25 to 50 transistors per inch range.